Scroll compressor and method of manufacturing the same

ABSTRACT

A scroll compressor includes a fixed scroll including a spiral unit, an orbiting scroll including a spiral unit and combined with the spiral unit of the fixed scroll to form a compression chamber for compressing refrigerant, a main shaft for transmitting drive power to the orbiting scroll, an electric motor unit configured to rotate the main shaft, and a first balancer for compensating unbalance of the orbiting scroll with respect to a rotation center of the main shaft. The first balancer has an outline in a cylinder shape, and includes a high-density part made of a high-density material, and a low-density part made of a low-density material having a density lower than a density of the high-density material.

TECHNICAL FIELD

The present invention relates to a scroll compressor and a method ofmanufacturing the same, and particularly relates to the structure of abalancer.

BACKGROUND ART

Conventionally, two balancers or more have been attached to a main shaftof a scroll compressor to compensate centrifugal force of aneccentrically orbiting spiral of oscillatory movement. Each balancerhas, for example, a semi-circular shape or a fan shape in plan view toachieve eccentricity of a barycenter. Thus, rotation of the balanceragitates surrounding fluid, causing the following problems.

When the balancer is arranged below a main bearing, oil dropped from themain bearing is scattered in the form of mist by rotation of thebalancer and is moved to the compressor together with refrigerant,resulting in an increase of oil loss. When the balancer is arranged in aframe above the main bearing, the balancer rotates in a space filledwith oil, which leads to power loss due to agitation of the oil.

To solve the above-described problems, a scroll compressor is disclosedin which the agitation of fluid by the balancer is prevented (forexample, refer to Patent Literature 1).

In Patent Literature 1, the balancer has an outline in a cylinder shapethat is circular in plan view, and a hollow space is provided in thebalancer to secure centrifugal force necessary for balancing with thecentrifugal force of the orbiting spiral, and prevent agitation ofsurrounding fluid.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Laid-open No. 2002-031070 (forexample, refer to [0016] and FIG. 2)

SUMMARY OF INVENTION Technical Problem

However, in Patent Literature 1, the hollow space is provided insideeach balancer to achieve the eccentricity of its barycenter, and thus,when the balancer is disposed in a space filled with oil, the oil flowsinto the hollow space. This leads to a difference in the centrifugalforce generated to the balancer from a designed value, causing a problemof increasing vibration.

The present invention is intended to solve the above-described problems,and it is an object of the present invention to provide a scrollcompressor capable of preventing agitation of fluid and an increase invibration, and a method of manufacturing the same.

Solution to Problem

A scroll compressor according to one embodiment of the present inventionincludes a fixed scroll including a spiral unit, an orbiting scrollincluding a spiral unit and combined with the spiral unit of the fixedscroll to form a compression chamber for compressing refrigerant, a mainshaft for transmitting drive power to the orbiting scroll, an electricmotor unit configured to rotate the main shaft, and a first balancer forcompensating unbalance of the orbiting scroll with respect to a rotationcenter of the main shaft. The first balancer has an outline in acylinder shape, and includes a high-density part made of a high-densitymaterial, and a low-density part made of a low-density material having adensity lower than a density of the high-density material,

Advantageous Effects of Invention

In a scroll compressor according to one embodiment of the presentinvention, a balancer has an outline in a cylinder shape, which canprevent agitation of surrounding fluid when the balancer rotates.Moreover, no hollow space for eccentricity of a barycenter is providedinside the balancer, causing no difference in centrifugal forcegenerated to the balancer from a designed value, and preventing anincrease in vibration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a vertical sectional view of a scroll compressor according toEmbodiment 1 of the present invention.

FIGS. 2(a) and 2(b) are each a diagram illustrating a low-density partof a first balancer of the scroll compressor according to Embodiment 1of the present invention.

FIGS. 3(a) and 3(b) are each a diagram illustrating a method ofassembling the first balancer of the scroll compressor according toEmbodiment 1 of the present invention.

FIG. 4 is an enlarged view of the vicinity of a balancer-attached sliderASSY of a scroll compressor according to Embodiment 2 of the presentinvention.

FIGS. 5(a) and 5(b) are each a diagram illustrating thebalancer-attached slider ASSY of the scroll compressor according toEmbodiment 2 of the present invention.

FIG. 6 is a diagram illustrating prevention of turnover of thebalancer-attached slider ASSY of the scroll compressor according toEmbodiment 2 of the present invention.

FIG. 7 is a vertical sectional view of a scroll compressor according toEmbodiment 3 of the present invention.

FIGS. 8(a) and 8(b) are each a diagram illustrating a method ofattaching, to a rotor, a second balancer of the scroll compressoraccording to Embodiment 3 of the present invention.

FIG. 9 is an enlarged view of the vicinity of the second balancer of thescroll compressor according to Embodiment 3 of the present invention.

FIG. 10 is a vertical sectional view of a scroll compressor according toEmbodiment 4 of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below withreference to the accompanying drawings. Those embodiments describedbelow are not intended to limit the present invention. A relationbetween the sizes of components in the drawings described below isdifferent from the actual relation in some cases.

Embodiment 1

The following first describes the structure of a scroll compressor 100according to the present Embodiment 1.

FIG. 1 is a vertical sectional view of the scroll compressor 100according to Embodiment 1 of the present invention.

The scroll compressor 100 is configured to suck and compress refrigerantcirculating in a refrigeration cycle, and discharge the refrigerant athigh temperature and high pressure. As illustrated in FIG. 1, the scrollcompressor 100 includes a compression mechanism unit and an electricmotor unit in a shell, where the compression mechanism unit is arrangedon an upper side, and the electric motor unit is arranged on a lowerside.

The shell is a pressure resisting container including a middle shell 25having a cylinder shape, a lower shell 26 sealed to an opening on alower surface of the middle shell 25 by, for example, welding, and anupper shell 24 sealed to an upper surface opening of the middle shell 25by, for example, welding.

The middle shell 25 is connected with a suction pipe 7 formed as part ofa refrigerant circuit and configured to suck the refrigerant into theshell, and includes a frame 6 fixed to an inner periphery of an upperend part, and a stator 11 fixed to an inner periphery of a middle part.A bottom part of the lower shell 26 serves as an oil reservoir 18 thataccumulates therein oil for lubricating each bearing. A bottom surfaceof the frame 6 is connected with an oil discharge pipe 8 for returningoil accumulated in the frame 6 to the oil reservoir 18. The upper shell24 is connected with a discharge pipe 1 for discharging compressedrefrigerant from the shell to the refrigerant circuit.

The compression mechanism unit includes at least a fixed scroll 4provided with a spiral unit 4 a on one of its surfaces, an orbitingscroll 5 provided with, on one of its surfaces, a spiral unit 5 a havinga spiral direction opposite to that of the fixed scroll 4, an orbitingbearing 21 provided opposite to a compression chamber with reference tothe orbiting scroll 5 and supported to orbit freely by an eccentricslider shaft portion 14 a, the frame 6 to which the fixed scroll 4 isfixed and that is provided with a main bearing 19 in a central part, anda main shaft 14 through which a rotor 12 adhered to an outer peripherytransmits drive power to the orbiting scroll 5. The compressionmechanism unit is coupled with the electric motor unit and configured tocompress the refrigerant.

The eccentric slider shaft portion 14 a is a slider mounting shaftinstalled on an upper part of the main shaft 14 to achieve eccentricityof a slider 22 with respect to the main shaft 14.

The spiral units 4 a and 5 a are combined with each other to form aplurality of compression chambers (not illustrated) between the fixedscroll 4 and the orbiting scroll 5. To reduce refrigerant leaked from anapical surface of the spiral unit 4 a of the fixed scroll 4 and anapical surface of the spiral unit 5 a of the orbiting scroll 5, sealing(not illustrated) is provided to the apical surface of the spiral unit 4a of the fixed scroll 4 and the apical surface of the spiral unit 5 a ofthe orbiting scroll 5.

A discharge port 28 for discharging refrigerant gas compressed to highpressure is formed in a central part of the fixed scroll 4. Therefrigerant gas compressed to high pressure is ejected into a highpressure part (not illustrated) in the upper shell 24. The refrigerantgas ejected into the high pressure part is discharged into therefrigeration cycle through the discharge pipe 1. The discharge port 28is provided with a discharge valve 29 for preventing backflow ofrefrigerant from the high pressure part to the discharge port 28.

The electric motor unit includes the rotor 12 fixed to the main shaft 14and the stator 11 fixed to the middle shell 25. The electric motor unitis configured to be driven at start of power supply to the stator 11 androtate the main shaft 14, causing the orbiting scroll 5 to performorbiting movement through the main shaft 14.

The scroll compressor 100 includes a thrust plate 30 as a thrust bearingthat supports the orbiting scroll 5 in an axial center direction, anOldham's coupling 23 supported to orbit freely by the frame 6 to preventspin of the orbiting scroll 5 and provide orbiting movement, the slider22 that supports the orbiting scroll 5 to allow the orbiting scroll 5 toorbit, a sleeve 20 provided near the eccentric slider shaft portion 143to smoothly rotate the main bearing 19 of the frame 6 and the main shaft14, and a first balancer 27 and a second balancer 13 for compensatingunbalance of the orbiting scroll 5 performing orbiting movement throughthe eccentric slider shaft portion 14 a, with respect to a rotationcenter of the main shaft 14. The first balancer 27 is provided above theelectric motor unit, whereas the second balancer 13 is provided belowthe electric motor unit.

The main shaft 14 rotates with rotation of the rotor 12 to cause theorbiting scroll 5 to orbit. The upper part of the main shaft 14 issupported by the main bearing 19 formed in the frame 6. A lower part ofthe main shaft 14 is rotatably supported by a sub bearing 16 formed in acentral part of a sub frame 15 provided to a lower part of the shell.The sub bearing 16 has its outer ring fitted by pressing in a bearinghousing part formed in the central part of the sub frame 15.

The sub frame 15 is provided with a displacement oil pump 17 configuredto pump oil from the oil reservoir 18 in the bottom part of the shelland supply the oil to each sliding unit, and a pump shaft portion 14 bfor transmitting rotational force to the oil pump 17 is integrallyformed the main shaft 14.

The main shaft 14 includes inside a vertical lubricating hole 14 c thatpenetrates from a lower end of the pump shaft portion 14 b to an upperend of the eccentric slider shaft portion 14 a in the vertical direction(axial direction) and supplies oil o bearings and sliding units of thecompression mechanism unit.

The first balancer 27 includes a high-density part 10 and a low-densitypart 9 having a density lower than that of the high-density part 10, andis formed by attaching the high-density part 10 to the low-density part9. The first balancer 27 has an outline in a cylinder shape not toagitate surrounding fluid when rotating. The high-density part 10 ismade of a high-density material such as metal, and the low-density part9 is made of a low-density material such as resin material. With thisconfiguration, the first balancer 27 has a barycenter that is eccentrictoward the high-density part 10, and is capable of generatingcentrifugal force necessary as a balancer. The first balancer 27 issubstantially solid inside and has an extremely small hollow space toprevent generation of a difference in centrifugal force due to oilflowed into the first balancer 27.

The following describes an operation of the scroll compressor 100.

In the scroll compressor 100 configured as described above, when thestator 11 is supplied with power, the rotor 12 is rotated by rotationalforce from a rotating magnetic field generated by the stator 11, and themain shaft 14 is rotated by the rotation of the rotor 12.

When the main shaft 14 is rotated, the eccentric slider shaft portion 14a is rotated in the orbiting bearing 21 through the slider 22,transmitting drive power to the orbiting scroll 5. Simultaneously, theorbiting scroll 5 performs orbiting movement while being prevented fromspinning by the Oldham's coupling 23 reciprocating inside an Oldhamgroove (not illustrated) of the orbiting scroll 5 housing a key part(not illustrated) formed on one of surfaces of the Oldham's coupling 23,and an Oldham groove (not illustrated) of the frame 6 housing a key part(not illustrated) formed on the other surface of the Oldham's coupling23. The frame 6 and the sub frame 15 are fixed inside the shell, andthus an accuracy variation of the fixation and an accuracy variation inan individual component lead to an axial center difference between themain bearing 19 and the sub bearing 16. Because of these accuracyvariations as well as deflection of the main shaft 14, the main bearing19 and the main shaft 14, and the sub bearing 16 and the main shaft 14are not always parallel to each other.

To provide parallelism to a sliding surface of the main bearing 19, thesleeve 20 is housed between the main shaft 14 and the main bearing 19.When the axial center difference exits between the main bearing 19 andthe sub bearing 16, the main shaft 14 is tilted to the main bearing 19,but this tilt of the main shaft 14 is canceled by a pivot part (notillustrated) of the main shaft 14 in contact with an inner periphery ofthe sleeve 20. Accordingly, an outer periphery of the sleeve 20 isalways slidable in parallel with the main bearing 19.

Centrifugal force is generated to the orbiting scroll 5 by its orbitingmovement, causing the eccentric slider shaft portion 14 a of the mainshaft 14 to slide within a slidable range of a sliding surface (notillustrated) of the slider 22. Then, the spiral unit 5 a of the orbitingscroll 5 and the spiral unit 4 a of the fixed scroll 4 become in contactwith each other to form a compression chamber. The centrifugal force ofthe orbiting scroll 5 and a load in the radial direction generated tocompress refrigerant act on the eccentric slider shaft portion 14 a ofthe main shaft 14, and accordingly, in some cases, the eccentric slidershaft portion 14 a becomes deflected to be not parallel to an innersurface of the orbiting bearing 21 provided in a central part of a lowersurface of the orbiting scroll 5.

To provide parallelism to a sliding surface in the orbiting bearing 21,the slider 22 is housed between the eccentric slider shaft portion 14 aof the main shaft 14 and the orbiting bearing 21. Thus, the tilt of theeccentric slider shaft portion 14 a of the main shaft 14 with respect tothe orbiting bearing 21, which is caused by the deflection of theeccentric slider shaft portion 14 a, is canceled by a pivot part (notillustrated) of the eccentric slider shaft portion 14 a in contact withthe sliding surface of the slider 22. Accordingly, an outer periphery ofthe slider 22 is always slidable in parallel with the orbiting bearing21.

The refrigerant in the refrigerant circuit is sucked into the shellthrough the suction pipe 7, and flows, through a suction port (notillustrated) of the frame 6, into the compression chamber formed by thespiral unit 5 a of the orbiting scroll 5 and the spiral unit 4 a of thefixed scroll 4. The compression chamber is moved toward the center ofthe orbiting scroll 5 by the orbiting movement of the orbiting scroll 5,and the refrigerant is thereby reduced in volume to be compressed. Inthis process, the compressed refrigerant applies a load to separate thefixed scroll 4 and the orbiting scroll 5 from each other, but this loadon the orbiting scroll 5 is supported by a bearing formed by theorbiting bearing 21 and the thrust plate 30. The compressed refrigerantpasses through the discharge port 28 of the fixed scroll 4, pushes toopen the discharge valve 29, and passes through the high pressure partin the upper shell 24, before being discharged from the shell to therefrigerant circuit through the discharge pipe 1.

In the above-described series of operations, the oil pump 17 is drivenby the pump shaft portion 14 b of the main shaft 14 in rotation to pumpoil from the oil reservoir 18 at the bottom part of the shell throughthe vertical lubricating hole 14 c. The pumped oil is supplied to themain bearing 19, the sub bearing 16, and the orbiting bearing 21. Then,the oil lubricates the main bearing 19 and the sub bearing 16 and dropsdown back to the oil reservoir 18 at the bottom of the shell. Oil havinglubricated the orbiting bearing 21 is stored in a space 6 a in theframe. The oil in the space 6 a in the frame is supplied to the thrustbearing, the Oldham's coupling 23, the spiral units 4 a and 5 a, and themain bearing 19, and also used to, for example, cool the orbitingbearing 21 and the main bearing 19. The space 6 a in the frame isprovided with the oil discharge pipe 8, through which excessive oil isreturned to the oil reservoir 18 at the bottom part of the shell fromthe space 6 a in the frame.

The following describes the first balancer 27 according to the presentEmbodiment 1.

FIGS. 2(a) and 2(b) are each a diagram illustrating the low-density part9 of the first balancer 27 of the scroll compressor 100 according toEmbodiment 1 of the present invention. FIG. 2(a) is a plan view of thelow-density part 9 of the first balancer 27, and FIG. 2(b) is asectional view taken along line A-A in FIG. 2(a).

The low-density part 9 of the first balancer 27 includes a low-densitymain part 9 c and a cover part 9 d, and is provided with a shaft hole 9a through which the main shaft 14 is provided, a high-density parthousing hole 9 b for housing the high-density part 10, and a low-densitypart fastening hole 9 e for fastening with the high-density part 10. Thelow-density part 9 has an outline in a cylinder shape with hollowedparts corresponding to the shaft hole 9 a, the high-density part housinghole 9 b, and the low-density part fastening hole 9 e.

FIGS. 3(a) and 3(b) are each a diagram illustrating a method ofassembling the first balancer 27 of the scroll compressor 100 accordingto Embodiment 1 of the present invention. FIG. 3(a) illustrates thefirst balancer 27 before assembly, and FIG. 3(b) illustrates the firstbalancer 27 after assembly.

A high-density part fastening hole 10 a for fastening with thelow-density part 9 is formed in the high-density part 10 of the firstbalancer 27, and the high-density part 10 is fitted into thehigh-density part housing hole 9 b of the low-density part 9 whilepositions of the high-density part fastening hole 10 a and thelow-density part fastening hole 9 e of the low-density part 9 arealigned. In this fitting, it may be preferable to have a clearance of 1mm or less between the high-density part 10 and the high-density parthousing hole 9 b of the low-density part 9 to uniquely determine thepositional relation between the high-density part 10 and the low-densitypart 9 without a large variation. After the fitting, the low-densitypart 9 and the high-density part 10 are fastened to the low-density partfastening hole 9 e and the high-density part fastening hole 10 a througha first fastening member 2 such as a bolt or a rivet.

The high-density part 10 is supported by the low-density part 9 throughfrictional force between the cover part 9 d of the low-density part 9and a fastening surface of the high-density part 10, and thus,centrifugal force generated by the first balancer 27 in rotationprevents shifting of the low-density part 9 and the high-density part 10from each other. This can prevent oil from flowing into the firstbalancer 27, thereby preventing a difference in centrifugal force.

As described above, the first balancer 27 according to the presentEmbodiment 1 has an outline in a cylinder shape, and thus can preventagitation of surrounding fluid when rotating. The first balancer 27includes the low-density part 9 and the high-density part 10, and thushas a barycenter that is eccentric toward the high-density part 10,thereby generating centrifugal force necessary as a balancer. Theconfiguration of the first balancer 27 is substantially solid inside andhas a small hollow space, preventing generation of a difference incentrifugal force due to oil flowing into the first balancer 27. Thiscan prevent a difference in centrifugal force generated to the balancerfrom a designed value, and prevent an increase in vibration.

Embodiment 2

The following describes the present Embodiment 2. Any descriptionduplicating with that in Embodiment 1 will be omitted, and any partidentical or equivalent to that in Embodiment 1 will be denoted by thesame reference numeral.

FIG. 4 is an enlarged view of the vicinity of a balancer-attached sliderASSY 40 of the scroll compressor 100 according to Embodiment 2 of thepresent invention. FIGS. 5(a) and 5(b) are each a diagram illustratingthe balancer-attached slider ASSY 40 of the scroll compressor 100according to Embodiment 2 of the present invention. FIG. 5(a) is a sideview of the balancer-attached slider ASSY 40, and FIG. 5(b) is asectional view taken along line B-B in FIG. 5(a).

In the present Embodiment 2, the compression mechanism unit is providedwith the balancer-attached slider ASSY 40. The balancer-attached sliderASSY 40 includes a balancer-attached slider 40 a in which a slider 40 dis attached to a high-density balancer 40 f, and a low-density part 40 battached to the balancer-attached slider 40 a. The balancer-attachedslider 40 a rotates in a space filled with oil, and thus reduction in anoil scattering loss can be achieved by attaching the low-density part 40b to the balancer-attached slider 40 a.

As illustrated in FIGS. 5(a) and 5(b), the low-density part 40 b isattached to the balancer-attached slider ASSY 40 to cover thehigh-density balancer 40 f. The balancer-attached slider 40 a isprovided with an oil drain gap 40 c having a dimension of about 0.5 mmto 3 mm for draining oil leaking from a lower part of the orbitingbearing 21. When provided near a lower end of the orbiting bearing 21,the oil drain gap 40 c allows efficient drain of the oil through ashortest flow path. An eccentric slider fitting hole 40 e for fittingwith the eccentric slider shaft portion 14 a is provided in a centralpart of the balancer-attached slider ASSY 40.

Fig, 6 is a diagram illustrating prevention of turnover of thebalancer-attached slider ASSY 40 of the scroll compressor 100 accordingto Embodiment 2 of the present invention.

When a parallel sliding bearing is used as the orbiting bearing 21, anaction central point of orbiting bearing reaction force exists at aposition in a height direction of the center of the orbiting bearing 21.When a position in a height direction of an action central point ofcentrifugal force of the entire balancer-attached slider ASSY 40 is setto be equal to the position in the height direction of the center of theorbiting bearing, the centrifugal force (arrow α 41) and the orbitingbearing reaction force (arrow β 42) act at the same position in theheight direction, preventing generation of a moment to turn over thebalancer-attached slider ASSY 40. This configuration can prevent partialcontact of the orbiting bearing 21, thereby securing the reliability ofthe orbiting bearing 21. When the balancer-attached slider 40 a iscovered by a hollow cover, centrifugal force applied to oil flowing intothe cover adversely generates a moment to turn over thebalancer-attached slider 40 a, which is, however, not the case with thepresent Embodiment 2.

Embodiment 3

The following describes the present Embodiment 3. Any descriptionduplicating with that in Embodiment 1 will be omitted, and any partidentical or equivalent to that in Embodiment 1 will be denoted by thesame reference numeral.

FIG. 7 is a vertical sectional view of the scroll compressor 100according to Embodiment 3 of the present invention.

In the present Embodiment 3, as illustrated in FIG. 7, the secondbalancer 13 includes a high-density part 52 and a low-density part 51having a density lower than that of the high-density part 52.

Even when the scroll compressor 100 is operated while refrigerant isaccumulated and the second balancer 13 is immersed in a mixture ofliquid refrigerant and oil, the oil and the liquid refrigerant do notflow into the second balancer 13, causing no difference in centrifugalforce of the second balancer 13 from a designed value, and preventing anincrease in vibration.

FIGS. 8(a) and 8(b) are each a diagram illustrating a method ofattaching, to the rotor 12, the second balancer 13 of the scrollcompressor 100 according to Embodiment 3 of the present invention. FIG.8(a) is a plan view of the second balancer 13, and FIG. 8(b) is a sideview of the second balancer 13.

A high-density part fastening hole 52 a is formed in the high-densitypart 52 of the second balancer 13, and a low-density part fastening hole51 a is formed in the low-density part 51 of the second balancer 13. Ashaft hole 50 is formed by the high-density part 52 and the low-densitypart 51. A second fastening member 3 such as a bolt or a rivet isprovided through the high-density part fastening hole 52 a and thelow-density part fastening hole 51 a to swage the high-density part 52and the low-density part 51 together with the rotor 12, therebyattaching the second balancer 13 to the rotor 12. This assembly canachieve a high productivity.

FIG. 9 is an enlarged view of the vicinity of the second balancer 13 ofthe scroll compressor 100 according to Embodiment 3 of the presentinvention.

As illustrated in FIG. 9, the second balancer 13 including thehigh-density part 52 and the low-density part 51 may be providedseparately from the rotor 12 at a position closer to the sub bearing 16than the rotor 12. With this configuration, the centrifugal force of theorbiting scroll 5 can be compensated even when the first balancer 27 andthe second balancer 13 are downsized. When positioned at a lowerposition, the second balancer 13 is likely to be immersed into oil.Since the second balancer 13 is solid and has an outline in a cylindershape, however, no oil scattering nor increase in vibration is causedunlike a case in which only a second balancer in a semi-cylinder shapeis provided.

Embodiment 4

The following describes the present Embodiment 4. Any descriptionduplicating with that in Embodiment 1 will be omitted, and any partidentical or equivalent to that in Embodiment 1 will be denoted by thesame reference numeral.

FIG. 10 is a vertical sectional view of the scroll compressor 100according to Embodiment 4 of the present invention. In the presentEmbodiment 4, as illustrated in FIG. 10, the first balancer 27 isprovided below the main bearing 19. Embodiment 4 differs in the positionof the first balancer 27 from Embodiment 1 in which the first balancer27 is provided above the main bearing 19 as illustrated in FIG. 1.However, the same effect as that of Embodiment 1 is obtained with thisposition in the present Embodiment 4.

REFERENCE SIGNS LIST

1 discharge pipe 2 first fastening member 3 second fastening member 4fixed scroll 4 a spiral unit (fixed scroll) 5 orbiting scroll 5 a spiralunit (orbiting scroll) 6 frame 6 a space in the frame 7 suction pipe 8oil discharge pipe 9 low-density part (first balancer) 9 a shaft hole 9b high-density part housing hole 9 c low-density main part 9 d coverpart 9 e low-density part fastening hole 10 high-density part 10 ahigh-density part fastening hole 11 stator 12 rotor 13 second balancer14 main shaft 14 a eccentric slider shaft portion 14 b pump shaftportion 14 c vertical lubricating hole 15 sub frame 16 sub bearing 17oil pump oil reservoir 19 main bearing 20 sleeve 21 orbiting bearing 22slider 23 Oldham's coupling 24 upper shell 25 middle shell 26 lowershell 27 first balancer 28 discharge port 29 discharge valve 30 thrustplate 40 balancer-attached slider ASSY 40 a balancer-attached slider 40b low-density part 40 c oil drain gap 40 d slider 40 e eccentric sliderfitting hole 40 f balancer 50 shaft hole 41 arrow α 42 arrow β 51low-density part (second balancer) 51 a low-density part fastening hole52 high-density part (second balancer) 52 a high-density part fasteninghole 100 scroll compressor

1. A scroll compressor comprising: a fixed scroll including a spiralunit; an orbiting scroll including a spiral unit and combined with thespiral unit of the fixed scroll to form a compression chamber forcompressing refrigerant; a main shaft for transmitting drive power tothe orbiting scroll; an electric motor unit configured to rotate themain shaft; and a first balancer for compensating unbalance of theorbiting scroll with respect to a rotation center of the main shaft, thefirst balancer having an outline in a cylinder shape, and including ahigh-density part made of a high-density material, and a low-densitypart made of a low-density material having a density lower than adensity of the high-density material, the low-density part covering anouter peripheral surface of the high-density part.
 2. The scrollcompressor of claim 1, wherein the low-density part of the firstbalancer includes a shaft hole through which the main shaft is provided,a high-density part housing hole for housing the high-density part, anda low-density part fastening hole for fastening with the high-densitypart, the high-density part of the first balancer includes ahigh-density part fastening hole for fastening with the low-density partof the first balancer, and positions of the high-density part fasteninghole of the first balancer and the low-density part fastening hole ofthe first balancer are aligned, and the high-density part of the firstbalancer and the low-density part of the first balancer are fastened toeach other through a first fastening member with the high-density partof the first balancer being fitted into the high-density part housinghole.
 3. The scroll compressor of claim 1, wherein the first balancer isprovided above the electric motor.
 4. The scroll compressor of claim 1,further comprising a slider supporting the orbiting scroll, wherein thefirst balancer is attached to the slider.
 5. The scroll compressor ofclaim 1, further comprising a second balancer provided below theelectric motor unit for compensating unbalance of the orbiting scrollwith respect to the rotation center of the main shaft, wherein thesecond balancer has an outline in a cylinder shape, and includes ahigh-density part made of a high-density material, and a low-densitypart made of a low-density material having a density lower than adensity of the high-density material.
 6. The scroll compressor of claim5, further comprising a sub bearing supporting a lower part of the mainshaft, wherein the second balancer is provided at a position closer tothe sub bearing than the electric motor unit.
 7. The scroll compressorof claim 5, wherein the electric motor unit includes a rotor and astator, the low-density part of the second balancer is provided with alow-density part fastening hole for fastening with the rotor, thehigh-density part of the second balancer is provided with a high-densitypart fastening hole for fastening with the rotor, and the high-densitypart of the second balancer and the low-density part of the secondbalancer are fastened to the rotor through a second fastening member. 8.A method of manufacturing the scroll compressor of claim 2, comprisingassembling the first balancer by aligning the positions of thehigh-density part fastening hole of the first balancer and thelow-density part fastening hole of the first balancer, fitting thehigh-density part of the first balancer into the high-density parthousing hole, and fastening the high-density part of the first balancerand the low-density part of the first balancer through the firstfastening member.
 9. A method of manufacturing the scroll compressor ofclaim 7, comprising attaching the second balancer to the rotor byfastening the high-density part of the second balancer and thelow-density part of the second balancer to the rotor through the secondfastening member.
 10. The scroll compressor of claim 1, wherein thelow-density part comprises a resin material.
 11. The scroll compressorof claim 4, wherein the slider includes an oil drain gap for drainingoil.
 12. The scroll compressor of claim 11, further comprising anorbiting bearing provided opposite to the compression chamber withreference to the orbiting scroll, and supported to orbit freely by aneccentric slider shaft portion installed on an upper part of the mainshaft, wherein the oil drain gap is provided below a lower end of theorbiting bearing.
 13. The scroll compressor of claim 12, wherein theorbiting bearing comprises a parallel sliding bearing, and the slider isarranged such that a position in a height direction of an action centralpoint of centrifugal force of the entire slider is set to be equal to aposition in a height direction of a center of the orbiting bearing.